Quiet operating quick-break mechanism for load tap changing transformer



Oct. 29, 1957 BAGUHN 2,811,595

QUIET OPERATING QUICK-BREAK MECHANISM FOR LOAD TAP CHANGING TRANSFORMER Filed Aug. 1, 1955 2 Sheets-Sheet 1 gag/1 c] m ve vdcori A. H. BAGUHN 2,811,595 QUIET GPERATING QUICK-BREAK MECHANISM FOR LOAD TAP CHANGING TRANSFORMER Oct. 29, 1957 2 Sheets-Sheet 2 Filed Aug. 1, 1955 United States Patent 01 QUIET OPERATING QUICK-BREAK MECHANESM FOR LOAD TAP CHANGING TRANSFORMER Alfred H. Baguhn, West Allis, Wis., assignor to Allis- Chalmers Manufacturing Company, Milwaukee, Wis.

Application August 1, 1955, Serial No. 525,619

7 Claims. (Cl. 20017) This invention relates in general to load tap changing transformer having a dial type switch and an actuating mechanism for imparting a quick-break, quick-make step movement to the movable contacts of the switch, and in particular to an improved actuating mechanism which is extremely quiet in operation.

Load tap changing transformers are used quite extensively in the distribution of electrical energy, their purpose being to maintain the voltage which is supplied to the consumer at a reasonably constant voltage regardless of load changes on the system. In recent years because of the rapid increase in the need for more electrical power, existing installations of load tap changing transformers were found to be inadequate. Where previously one installation was sufficient to serve the demands of a community, utilities soon realized that the one installation was too remote from the load center to economically serve its purpose. The utilities were then faced with the problem of installing additional load tap changing transformers in already built up communitites, and in locations where the ambient noise levels were considerably below that of the standard tap changing transformer. As a result, various complaints were received from persons living near the new installations that the noise level of the tap changing mechanism was annoying. Utilities therefore demanded tap changing under load transformers which could operate below previously acceptable noise levels for installation at these subnormal noise locations.

The mechanical and electrical structural requirements of a tap changing under load transformer do not readily lend themselves to quiet operation. Because taps are changed under load, the switching action should be made in a short quick step in order to reduce contact deterioration due to arcing. In addition, contact pressure between the movable contacts and the stationary contacts should be relatively large in order to insure low contact resistance. Further, the various moving parts must have a relatively large mass since they must be mechanically strong to withstand years of continuous operation with a minimum amount of servicing.

Previously suggested load tap changing transformers using dial type switches actuated by a quick-break mechanism have in the past proved quite successful from a mechanical and electrical standpoint. However, their noise level is not sufliciently low to permit their installation in these certain critical locations having a below normal ambient noise level.

It has been found, according to the present invention, that the operating noise level of the switch actuating mechanism may be considerably lowered by maintaining some of the movable parts which come in contact with each other under constant bias thereby eliminating the ambient pentrating noise caused by the fast moving parts coming in contact with each other.

It is therefore an object of the present invention to provide a load tap changing transformer having an improved tap changing switch actuating mechanism.

Another object of the present invention is to provide 2,811,595 Patented Oct. 29, 1957 ice an improved mechanism for actuating a dial type switch in short quick steps with a minimum of noise.

Objects and advantages other than those mentioned above will be apparent from the following description when read in connection with the drawing, in which:

Fig. 1 is a side view in elevation of a dial type switch and the improved actuating mechanism;

Fig. 2 is a front view in elevation of the switch and mechanism shown in Fig. 1 with parts broken away;

Figs. 3 and 4 are diagrammatical views of the spring assemblies shown in Fig. 1, illustrating the improved operation of the mechanism shown in Figs. 1 and 2.

Referring to the drawings, the tap changer shown in Figs. 1 and 2 comprises a dial type switch assembly and a quick-break mechanism. The dial switch assembly 11 comprises an insulating panel 13, a shaft 14 rotatably mounted in the panel with its axis of rotation normal to the face of the panel, a plurality of stationary contact members 15, and a pair of movable contact members 16. The stationary contact members 15 are mounted on panel 13 and circumferentially spaced on an arc of a circle having its center on the axis of rotation of the shaft 14. The movable contact members are fixedly mounted with respect to the shaft 14 and are rotatable therewith in the plane of the stationary contact members. Movable contact members 16 are spaced apart a distance corresponding to the circumferential spacing of the stationary contacts 15 and are arranged so that both movable contacts 16 may be disposed on one of the stationary contacts 15, or disposed in a bridging relationship with respect to two adjacent fixed contacts 15.

The switch actuating mechanism 12 includes a stationary index plate 20 supported in a vertical plane parallel to insulating panel 13 of the switch assembly 11 by suitable support members 21 and is provided with a plurality of circumferentially spaced notches 22, a shaft 23 which is rotatably mounted in the center of index plate 20 with its axis of rotation normal to the plane of the plate 20, a sprocket wheel 24 rotatably mounted on the shaft 23 parallel to the index plate 20 and an actuating member 26 fixedly mounted on the shaft 23 parallel to the sprocket wheel 24 and spaced axially therefrom.

The actuating mechanism further includes means 27 for driving the sprocket 24 at a relatively slow uniform continuous speed, a quick-break mechanism 28 for converting the relatively slow uniform speed of the sprocket into a snap action of the actuating member 26, and means 29 for translating the snap action of the actuating disk to the shaft 14 of the dial switch assembly 11 to impart a short quick step movement to the movable contact members 16.

As shown, the means 27 for driving the sprocket wheel comprises a motor 30 and a chain 31 but if desired, a gear arrangement or other known driving arrangement may be used.

The quick-break mechanism 28 for converting the slow continuous movement of the sprocket 24 to a snap action of the actuating disk 26 comprises a spring arrangement 33 and a latch device 34.

The spring arrangement 33 shown in detail in Figs. 3 and 4 comprises first and second spring assemblies 37 and 38, each comprising a main spring, an auxiliary spring, end plugs, a guide means, a. driving member, and a driven member.

The driving member 44 of each spring assembly as shown comprises a pin element 44a fixedly attached to the face of the sprocket 24 with the axis of the pin 44a normal thereto and spaced radially from the axis of the shaft 23 a predetermined distance. The driven member 45 of each spring assembly as shown also comprises a pin element 45a fixedly attached to the face of the actuating disk 26 with the axis of the pin normal thereto and spaced radially from the axis of the shaft another predetermined distance.

The pin elements 44:: and 45a extend into the axial spacing between the sprocket wheel 24 and the actuating disk 26 and may be considered to represent four corners of a trapezoid disposed in a plane normal to the shaft and intermediate the sprocket wheel and the actuating disk.

Since the spring assemblies are identical in construction only one is described. The guide means illustrated as a spring tube 43 is slightly longer than the length of a nonparallel side of the trapezoid and is provided with a stop element such as a spring separator disk 47 which is fixedly attached to the inner wall of the tube 43 dividing it into two spring receiving compartments 51 and 52. These compartments prevent the spring from buckling or from becoming misaligned and insures that their force will always be along a line connecting the driving pin and the driven pin. The main spring compartment 51 is longer in length than the auxiliary spring compartment 52 and is provided with a slot 53 in the wall portion extending from the open end of the compartment axially toward the separator disk 47. The distance between the end 54 of the slot 53 and the separator disk 47 is less than the compressed height of the main spring 40. The auxiliary spring compartment 52 is likewise provided with a similarly shaped slot 56 extending from the open end of the compartment towards the separator disk 47.

The slot 53 in the wall portion of the main spring compartment 51 is adapted to receive the driving member 44 of the assembly and the slot 56 in the wall portion of the auxiliary spring compartment 52 is adapted to re ceive the driven member 45. Since the driven member 45 and the driving member 44 of the assembly extend into the space between the sprocket 24 and the actuating disk 26 from opposite directions, the slots 53 and 56 in the two compartments 51 and 52 are on diametrically opposite sides of the tube 43.

The springs are disposed in their respective compart ments and the tubes 43 are positioned with their axes coincident with the nonparallel sides of the trapezoid, the slots 53 and 56 in the tubes 43 engaging the corresponding driving and driven members 44 and 45 of the assemblies. End plugs 42 are inserted at one end of each spring to provide a flat surface for the springs to act on.

When the actuating mechanism 12 is in the neutral position the distances between the driving members 44 and the driven members 45 of the respective assemblies 37 and 38 are substantially equal and the actuating disk 26 is in a state of balance.

A crank like member 60 connects the actuating disk to the shaft of the switch assembly and comprises a means for translating the snap action of the actuating disk 26 to the shaft 14 of the movable contacts.

In the preferred embodiment, all the springs are compression springs, the two main springs 40 having like spring constants and the two auxiliary springs 41 having like spring constants. The spring constants of the main spring 40 and auxiliary springs 41 are chosen so that with the mechanism in the balanced state, the auxiliary springs are fully compressed between the spring separator disk 47 and the driven member 45, and the main springs 40 are under a slight compression between the separator disk 47 and the driving member 44. A retaining pin 61 is inserted across the open end of the main spring compartment 51 to prevent the tube 43 from becoming disengaged from the driving member 44.

The latch device 34 comprises a latch member 66 which is pivotally mounted on a circumferential edge portion 67 of the actuating member 26. The latch member 66 extends through a suitable opening 68 in the sprocket 24 and engages one of the notches 22 of the stationary index plate corresponding to a position of the dial type switch. The latch member 66 is operated LED at a predetermined time by the edge portions 69 of the sprocket 26 which define the opening 68 through which the latch member 66 extends.

The operation of the improved tap changing under load transformers is as follows. The actuating mechanism i2 is shown in the deenergized position in Fig. 3, the quick-break mechanism being in a balanced condition and the latch 34 engaged in a notch 22 of the index plate 20. The movable contacts 16 are therefore in position with respect to the stationary contacts 15. Assuming it is desired to move the movable contacts 16 one step, the motor is energized either manually or automatically by a suitable control system and causes the sprocket 24 to rotate at a slow uniform speed in a clockwise direction, as shown in the drawing. The driven members 45 of the spring assemblies 37, 38 remain fixed inasmuch as the actuating disk 26 is held from turning by the engagement of the latch member 66 with the index plate 20. Rotation of the sprocket 24 starts to compress the main spring 40 of the left hand assembly 37 while the main spring 40 of the right hand assembly 33 is allowed to expand.

The main spring 40 of the right hand assembly 38 expands until the driving pin 44 comes in contact with the retaining pin 61 disposed across the open end of the main spring compartment 51 at which time the auxiliary spring 41 is still compressed. Further rotation of the sprocket 24- causes the spring tube 43 of the right hand assembly 38 to move with the driving pin 44 allowing the fully compressed auxiliary spring 41 to slowly expand. The end of the auxiliary spring 41 remains in contact with the stationary driven member 45. When the sprocket 24 has rotated a predetermined number of degrees the latch member 66 is disengaged, allowing the actuating disk 26 to move in accordance with the energy stored in the main spring 40 of the left hand assembly 37. This energy must be sutficient to overcome the friction between the movable contacts 16 and the stationary contacts 15, overcome the inertia of the actuating disk 26 and the moving contacts 16 and separate the moving contacts 16 from the stationary contacts 15 with a quick break to lessen the tendency of the contacts to are. The required amount of energy is adequately provided in the initial portion of the release cycle by the main spring 40 of the left hand assembly since there is relatively little force required in this portion of the cycle to compress the auxiliary spring 41 of the right hand assembly 38. Immediately after the latch member 66 is released, the energy in the main spring 40 acting on the driven member 45 causes the actuating disk 26 to move with a relatively fast step movement. The driven member 45 on the right hand assembly 38 at first compresses the auxiliary spring 41 flat and then moves the tube 43 with respect to the driving member 44 of the right hand assembly 38 to compress the main spring 40 of the right hand assembly. This recompression of the right hand main spring provides a snubbing action to slow up the movement of the actuating disk 26 after the movable contacts 16 have been separated from the stationary contacts 15. This snubbing action of the right hand main spring reduces the speed of the actuating disk 26 and allows the latch member 26 to drop into an adjacent notch 22 of the index plate 20 which corresponds to a new position of the switch 11. This operation is repeated if successive tap changes are required. Likewise, if the contacts 16 are to be moved in the other direction, the manner of operation is the same except that the actions of the left and right hand spring assemblies are reversed.

It will be seen that the noise level of the actuating mechanism is lowered considerably since the auxiliary spring 41 and the main spring 40 of the assembly 38 which does not store up the energy of the motor, cooperate with each other to maintain the parts of the assembly which come in contact with each other under a constant bias with respect to each other. Thus the ambient penetrating noise caused by a fast moving part coming in contact with another part is greatly reduced. For example, when the latch member 66 is released, the driven pin 45 of the right hand assembly quietly compresses the auxiliary spring 41 and the energy stored in the left hand main spring is then quietly absorbed by recompressing the right hand main spring until the latch member 66 engages the next notch 22 of the index plate 20.

While only one embodiment of the present invention has been illustrated and described it will be apparent to those skilled in the art that modifications other than that shown may be made Without departing from the spirit of the invention or from the scope of the appended claims.

It is claimed and desired to secure by Letters Patent:

1. A tap changing under load transformer including a dial type switch having a plurality of circumferentially spaced stationary contact positions and a pair of movable contacts, a mechanism for moving said movable contacts from one of said stationary contact positions to another of said stationary contact positions with a short quick-step movement to change the voltage of said transformer, said mechanism comprising an index plate provided with a plurality of spaced notches, a shaft rotatably mounted in the center of said plate, a sprocket member rotatably mounted on said shaft, an actuating member fixedly mounted on said shaft in axial spaced relationship with said sprocket member, means connecting said actuating member to said movable contacts, means for rotating said sprocket member at a relative slow uniform speed, and means for converting the relatively slow uniform speed of said sprocket to a rapid snap action of said actuating member to cause said movable contacts to move with a quick-step movement, said converting means comprising a pair of spring assemblies spaced symmetrically on opposite sides of said shaft and disposed between said members to act along force lines parallel to the fact of said members, and a latch device extending through a circumferentially elongated aperture in said sprocket member to engage one of said notches of said index plate to prevent rotation of said actuating member until said spring asesmblies are biased to a predetermined extent, each of said assemblies comprising means connecting the ends of said assembly to said members to provide relative movement between said assembly and said members, a main spring acting between said members along one of said force lines, a spring guide for maintaining the action of said main spring along said force line, and means cooperating between said guide and said connecting means to prevent a sudden impact therebetwcen resulting in substantially noiseless operation of said mechanism.

2. A mechanism for moving an element from one position to another with a quick-step movement comprising an index plate, a first member, means for rotating said first member about an axis at a relatively slow uniform speed, a second member, means connecting said second member to said element, means for rotating said second member about said axis with a rapid snap action to move said element comprising a pair of spring assemblies disposed between said members and latch means engageable with said index plate to prevent rotation of said second member until said assemblies are biased to a predetermined extent by rotation of said first member, each said assembly comprising a main spring disposed with its axis transverse to said axis of rotation of said members, guide means for said spring, means connecting the ends of said assembly to said members to provide relative movement between said guide means and said connecting means, and a compressed resilient element cooperating between said guide means and said connecting means to prevent a sudden impact between said guide means and said con necting means thereby resulting in substantially noiseless operation of said mechanism.

3. A mechanism for moving an element from one position to another with a quick-step movement comprising an index plate, a first member, means for rotating said first member about an axis at a relatively slow uniform speed, a second member, means connecting said second member to said element, means for rotating said second member about said axis with a rapid snap action to move said element comprising a pair of spring assemblies disposed between said member and latch means engageable with said index plate to prevent rotation of said second member until said assemblies are biased to a predetermined extent by rotation of said first member, each said assembly comprising a main spring disposed with its axis transverse to said axis of rotation of said members, guide means for said spring, a stop element fixed within said guide means, means connecting the ends of said assembly to said members to provide relative movement between said guide means and said connecting means, and an auxiliary spring acting within said guide means and between said stop element and said connecting means to prevent a sudden impact between said guide means and said connecting means thereby resulting in substantially noiseless operation of said mechanism.

4. A mechanism for moving an element from one position to another with a short quick-step movement, said mechanism comprising an index plate provided with a plurality of spaced notches corresponding to said positions, a shaft, a first member rotatably mounted on said shaft, a second member fixedly mounted on said shaft, means connecting said second member to said element to be moved, means for rotating said first member at a uniform speed, and means for converting the uniform speed of said first member to a rapid snap action of said second member to cause said element to move with a quick-step movement. said converting means comprising a pair of spring assemblies spaced symmetrically on opposite sides of said shaft and disposed between said members to act along force lines parallel to said members, and latch means engageable with one of said notches to prevent move ment of said second member until said spring assemblies are biased to a predetermined extent, each said assembly comprising a main spring acting between said members along one of said force lines, guide means for maintaining the action of said main spring along said force line, a stop element fixed within said guide means, and means connecting the ends of said assembly between said members to provide relative movement between said guide means and said connecting means, and means cooperating within said guide means and between said stop element and said connecting means to prevent a sudden impact between said guide means and said connecting means thereby resulting in substantially noiseless operation of said mechanism.

5. A mechanism for moving an element from one position to another with a short quick-step movement, said mechanism comprising an index plate provided with a plurality of circumferentially spaced notches corresponding to Said positions, a shaft, a sprocket member rotatably mounted on said shaft, an actuating member fixedly mounted on said shaft in axial spaced parallel relationship with said sprocket member, means connecting said actuating member to said element, means for rotating said sprocket at a relatively slow uniform speed, and means for converting the uniform speed of said sprocket member to a rapid snap action of said actuating member to cause said element to move with a quick-step movement. said converting means comprising a pair of spring assemblies spaced symmetrically on opposite sides of the portion of said shaft intermediate said members and disposed to act along force lines parallel to said members, and latch means engageable with one of said notches in said index plate to prevent movement of said actuating member until said spring assemblies are biased to a predetermined extent by rotation of said sprocket member, each said assembly comprising a main spring acting between said members along one of said force lines, a constant biasing auxiliary spring means in series with said main spring, guide means for maintaining the action to said main spring and said auxiliary means along said force line, a separator element within said guide and between said main spring and said auxiliary spring, and means connecting the ends of said assembly between said members to provide relative movement between said guide means and said connecting means.

6. In combination with a dial type switch having a plurality of circumferentially spaced stationary contacts and a movable contact, a mechanism for moving said movable contact from one of said stationary contacts to another of said stationary contacts with a short quickstep movement, said mechanism comprising an index plate provided with a plurality of spaced notches, a shaft rotatabiy mounted in the center of said plate, a sprocket member rotatably mounted on said shaft, an actuating member fixedly mounted on said shaft in axial spaced relationship with said sprocket member, means connecting said actuating member to said movable contact, means for rotating said sprocket member at a relative slow uniform speed, and means for converting the relatively shown uniform speed of said sprocket to a rapid snap action of said actuating member to cause said movable contact to move with a quick-step movement, said converting means comprising a pair of spring assemblies spaced symmetrically on opposite sides of said shaft and disposed between said members to act along force lines parallel to the face of said members, each of said assemblies comprising means connecting the ends of said assembly to said members to provide relative movement between said assembly and said members, a main spring acting between said members along one of said force lines, a spring guide for maintaining the action of said main spring along said force line, a separator element fixed within said spring guide and means cooperating within said guide and between said separator element and said connecting means to prevent a sudden impact between said guide and said connecting means resulting in substantially noiseless operation of said mechanism.

7. In combination with a dial type switch having a plu rality of circumferentially spaced stationary contacts and a movable contact, a mechanism for moving said movable contact from one of said stationary contacts to another of said stationary contacts with a short quick-step movement, said mechanism comprising an index plate provided with a plurality of spaced notches, a shaft rotatably mounted in the center of said plate, a sprocket member rotatably mounted on said shaft, an actuating member fixedly mounted on said shaft in axial spaced relationship with said sprocket member, means connecting said actuating member to said movable contact, means for rotating said sprocket member at a relative slow uniform speed, and means for converting the relatively slow uniform speed of said sprocket to a rapid snap action of said actuating member to cause said movable contact to move with a quick-step movement, said converting means comprising a pair of spring assemblies spaced symmetrically on opposite sides of said shaft and disposed between said members to act along force lines parallel to the face of said members, each of said assemblies comprising means connecting the ends of said assembly to said members to provide relative movement between said assembly and said members, said connecting means consisting of a first pin extending from the face of said sprocket member and a second pin extending from the face of said actuating member, a main spring acting between said members along one of said force lines, a spring guide for maintaining the action of said main spring along said force line, and spring means cooperating between said guide and said connecting means to prevent a sudden impact therebetween resulting in substantially noiseless operation of said mechanism.

References Cited in the file of this patent UNITED STATES PATENTS 

